This project was initiated to study the molecular genetics of cell cycle associated genes in C. neoformans. In 2003, we reported the function of the CCN1 gene which is necessary for cell growth at 37C. During 2004-2005,we studied the effect of TUP1 deletion on the biology of MATa and MATalpha strains in serotype D. TUP1 is a global regulator that controls morphogenesis in many ascomycetous fungi. Interestingly, tup1 mutants of C. neoformans exhibited quorum sensing (QS) and at growth temperatures that are conducive to QS function, a difference was observed between MATa and MATalpha strains. An 11-mer peptide secreted in the growth medium of tup1 mutant was identified as the quorum sensing molecule. Fungal QS factors reported thus far have been alcohols such as tyrosol or farnesol but a peptide has never been reported as a QS factor in the Kingdom Fungi.During 2005-2006, we deleted TUP1 from a serotype A strain of C. neoformans which differs from serotype D strains in capsular antigenicity and the function of various genes. Unlike in serotype D strains, the tup1 deletion in H99 caused no quorum sensning-like phenotype but the growth on complex media was clearly retarded compared to the wild type strains. Tup1 ko strain of serotype A showed a drastic increase in capsule formation and when the tup1 ko strains were complemented with the wild type TUP1 gene, the capsule size decreased significantly compared to the tup1 ko strains. These findings indicate that TUP1 represses capsule formation in vitro. The capsule size in vivo, however, was not affected by the TUP1 deletion. Mice infected with the tup1 ko strain survived much longer than either the wild type or the tup1 ko strain complemented with the TUP1 gene. In 2006-2007, we carried out microarray experiment to compare the differences in the expression of known or novel capsule related genes between the wild type and the tup1 ko strain.Interestingly,the microarray data indicated that expression of multiple genes related to iron homeostasis were affected by the deletion of the tup1. This could explain the cause of the observed hypercapsular phenotype of tup1 ko strain in serotype A background. A direct relationship between iron homeostasis and the degree of capsule formation is known to exist in Cryptococcus neoformans.